1. Technical Field
The present invention generally relates to a movable valve apparatus for an internal combustion engine. More specifically, the present invention relates to a movable valve apparatus for an internal combustion engine having a movable valve mechanism that changes the working condition of the air intake valve or exhaust valve depending on a supplied hydraulic pressure of the working fluid.
2. Description of Related Art
Japanese Laid-Open Patent Application H8-28219 discloses a movable valve mechanism that changes an opening/closing timing of an air intake or exhaust valve according to a supplied hydraulic pressure of working fluid. The hydraulic pressure supplied to this movable valve mechanism is adjusted according to a working condition of a spool that reciprocates within a sleeve of a hydraulic pressure control valve. The hydraulic pressure control valve includes a return spring that always biases the spool to a minus side, and a solenoid that drives the spool to the other side in response to an input of a control signal.
When a foreign object (impurity) such as chips that entered the working fluid during chip processing becomes jammed inside the hydraulic pressure control valve, particularly at a partition portion between a drain port formed in the sleeve and the spool, so-called valve lock may occur. Therefore, in the above-mentioned patent application, when it is determined that a foreign object is jammed, more specifically when an actual cam phase detected by a cam angle sensor and a target cam phase obtained by a separate calculation differ by more than a predetermined value, a foreign object removal operation is executed, during which the spool reciprocates temporarily.
In a valve timing adjustment apparatus disclosed in Japanese Laid-Open Patent Application H9-195805, the foreign object removal operation is executed when the hydraulic pressure control valve keeps an opening that is below a predetermined opening for longer than a predetermined period of time, when the engine is started or stopped, or while the engine is idling.
In view of the above, there exists a need for an improved movable valve apparatus for an internal combustion engine. This invention addresses this need for improvement in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
It has been determined from the disclosure of Japanese Laid-Open Patent Application H8-28219, which proposes executing the foreign object removal operation when a foreign object is actually jammed, that the targeted valve timing may not be achieved temporarily due to the foreign object removal operation, depending on the working condition of the spool at the time the foreign object removal operation is executed. Accordingly, malfunctioning such as insufficient acceleration and unstable idling may result.
Also, it has also been determined from Japanese Laid-Open Patent Application H8-28219 that the determination of a foreign object being jammed is made based on a phase difference in the cam phases. However, if this determination is made strictly, it may be mistakenly determined an occurrence of jamming even when it has not occurred. In that case, the spool reciprocates unnecessarily, reducing the responsiveness. On the other hand, when the determination is made leniently, it may be wrongfully determined that no jamming is occurring even when a foreign object is actually jammed. In that case, the working performance of the engine may be obstructed. In other words, lowering of engine output or engine stop may result.
On the other hand, in the Japanese Laid-Open Patent Application H9-195805, when the foreign object removal operation is executed in situations where a foreign object is likely to be jammed, the stability of the engine may be adversely affected if, for instance, the foreign object is jammed while the spool is returning to the initial position. Accordingly, further improvement is desired. The present invention is conceived in view of these problems.
An example of a movable valve mechanism is described in Japanese Laid-Open Patent Application H7-180514. This Japanese application describes a movable valve mechanism in which a phase of a camshaft of the air intake valve or the exhaust valve is changed relative to a crankshaft by a controller. The controller of this application operates a cam switching mechanism that switches a plurality of cams, and a mechanism that changes a working angle of the air intake valve (valve lift amount). In the aforementioned controller, an engine control unit has a memory or CPU that is preferably utilized to stores and executes various engine controls such as the aforementioned driving control of the spool, various controls of fuel injection period, fuel injection amount, and igniting timing.
Preferably, a port for supplying hydraulic pressure to the movable valve mechanism, a port for introducing the hydraulic pressure from the hydraulic pressure source, and a plurality of ports for draining are formed in the sleeve of the aforementioned hydraulic pressure control valve. These ports are selectively closed and opened based on the position of the spool, in order to adjust the supply of hydraulic pressure to the movable valve mechanism.
In this case, when it is determined that a foreign object is jammed while the spool is returning to the initial position, the spool cannot return to the initial position. In that case, the working condition (opening/closing timing) of the air intake or exhaust valve cannot return to the initial state. Accordingly, the engine may not idle or start properly, or the engine may stop. Therefore, the stability of the engine is dramatically lessened.
In accordance with one aspect of the present invention, a movable valve apparatus is provided for adjusting an air control valve of an internal combustion engine. The movable valve apparatus basically comprises a movable valve mechanism, a hydraulic pressure control valve and a controller. The movable valve mechanism is operatively controlled by hydraulic pressure of a working fluid to adjusting the air control valve. The hydraulic pressure control valve is operatively coupled to the movable valve mechanism to adjust the hydraulic pressure of the working fluid supplied to the movable valve mechanism. The hydraulic pressure control valve includes a spool reciprocally coupled within a sleeve to control the hydraulic pressure of the working fluid supplied to the movable valve mechanism. The controller is operatively coupled to the hydraulic pressure control valve to drive and control the spool within the sleeve. The controller is configured to execute a foreign object removal operation upon the controller determining that the spool is in a returning state in which the spool starts moving toward an initial position. The spool is temporarily reciprocated by the controller to remove foreign objects inside the hydraulic pressure control valve during the foreign object removal operation.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.